The global and national HIV/AIDS epidemic continues to expand, with half of new infections striking people under the age of 25. In the US, marginalized urban adolescents, particularly African-American and Hispanic youth, are at disproportionate risk. There is an urgent need for research that builds upon the expertise and experience of those engaged in adolescent HIV prevention efforts with large constituencies of diverse urban youth in order to develop the effective and adaptable strategies needed to stem the HIV epidemic. This study will examine whether specific characteristics of highly engaged program participation (e.g., youth voice/choice/influence on program decision-making, opportunities for individual development, and quality of linkages between the program and other key social microsystems, and program climate) influence young people's connectedness to family and the larger community, and their HIV risk reduction practices. We hypothesize that: (1) Highly engaged program participation and social connectedness are positively related; (2) Highly engaged program participation and high levels of social connectedness are each negatively related to measures of HIV risk behaviors; (3) Increases in active program participation and social connectedness over time are associated with reductions in HIV risk behaviors; (4) Part of the effect of program participation on HIV risk reduction is mediated through increases in social connectedness; and (5) Growth curves for participation, social connectedness and HIV risk reduction will vary as a function of program type (HIV prevention focused vs. other). In order to accomplish these aims, we will recruit a stratified sample of 400 13-17 year old adolescents joining New York City after-school programs (including programs focused specifically on HIV risk reduction) and conduct surveys with these youth at baseline and six and twelve months later. We will utilize latent growth models and structural equation models to assess changes over time and relationships among constructs, identify sub-groupings of adolescents with ' differentiated trajectories related to key constructs, explore mediating mechanisms, and examine the effects of program type on these empirical relationships. Relevance for public health: This study will investigate the extent to which highly engaged program participation may serve as a lever to increase social connectedness and reduce HIV-related risk behaviors. This requires the use of a new measure for participation, a promising but to date underspecified dimension of many health promotion and community development efforts. Evidence for the protective effects of highly engaged program participation and tools for its measurement in a variety of program contexts will assist community-based, multi-cultural programs to assess and improve their adolescent HIV prevention efforts. [unreadable] [unreadable] [unreadable] [unreadable] [unreadable] [unreadable] [unreadable]